It looks like the US Navy (who else?) will soon start using railguns on its vessels:
BAE Systems has delivered a functional, 32-megajoule Electro-Magnetic Laboratory Rail Gun (32-MJ LRG) to the U.S. Naval Surface Warfare Center in Dahlgren, Va. … Installation of the laboratory launcher is currently under way, and according to BAE, this is the first step toward the Navy’s goal of developing a tactical 64-megajoule ship-mounted weapon.
What exactly is a railgun? Well, picture how a piece of metal being attracted to a magnet. Now, imagine the magnet moving away from the piece of metal at just the right speed so that the piece of metal keeps going faster and faster, but never hits the magnet. Then, imagine the magnet disappears. What you have left is a piece of metal flying at an incredible speed — like a bullet, only much, much faster.
The railgun mentioned in the article can propel rounds up to eight times the speed of sound, which is more than twice the speed that most modern machineguns fire bullets at. This means more accuracy and longer range, and with the added benefit of not having to store explosive propellant (i.e. gunpowder).